The invention relates to the forming fabric for the forming area or wet end of a paper making machine. The forming fabric has at least two complete fabrics of any kind of binding which are jointly woven by binding yarns running in a longitudinal or machine direction and/or cross-machine direction so that the longitudinal yarns of the fabric are forming longitudinally directed fiber supporting points whereas the yarns in cross-machine direction are forming cross-machine direction fiber supporting points.
Multilayer sieves and compound fabrics, especially paper making fabrics the single layers of which are connected by a binding warp or a binding weft are well known in the art. Such fabrics are used for the manufacture of a multiplicity of kinds of paper, such as coarse papers and papers for cigarettes and condensors. It goes without saying that coarse papers, such as packing or wrapping papers must fulfill stability and tensile strength requirements completely more so than other requirements than for other papers such as cigarettes. The last mentioned papers are less critical with respect to the tensile strength but critical with respect to a defined permeability for air. On the other hand, the paper for newspapers or for printing purposes must fulfill special requirements with respect to their imprinting ability. These different requirements and demands are essentially influenced by the original paper forming process occurring in the forming area or wet part of a paper making machine. In that area the fibers of the pulp are generally uniformly distributed and directed as well as curled and matted together or clogged, whereas simultaneously the pulp is dewatered in order to develop the original fiber web. The surface structure of the forming fabric is therefore of absolute essential importance for the character of the paper to be manufactured.
On adapting the surface structure of the forming fabric to the special requirements the relationship of the fiber supporting points in longitudinal direction of the fibers and those fiber supporting points in fiber cross-machine direction is therefore of essential importance. By the term "fiber supporting point" all those fiber surface parts are understood to be extending uprightly away from the level of the sheet forming area of the forming fabric and in touch with the fibers of the pulp. In order to more clearly point out this matter attention is drawn to FIGS. 1 and 2 of the drawings showing known forming fabrics of paper making machines. These known fabrics are characterized with respect to FIG. 1 by an even relationship between the fiber supporting points in machine direction or longitudinal direction and cross-machine direction, i.e. these points are present in a relationship of 1:1, whereas according to FIG. 2 the fiber supporting points in machine direction dominate clearly those in cross machine direction, i.e. their number is greater.
In the past the influence of the fiber supporting points of those forming fabrics in a definite direction could only be changed by the fixing process of the fibers during which the related fiber supporting points could be put to a more or less prepositioned level, i.e. to a level adjacent to the paper sheet forming level in order to provide for those fiber supporting points during the sheet forming process the required dominating effect. This "shifting" of the fiber supporting points to a prepositioned level results, however, in essential disadvantages with respect to the quality of the paper to be manufactured. These disadvantages can result in the kind of the paper so strong that such a change of fiber supporting points can basically not be permitted. The essential drawbacks with respect to the quality are the diminishing of the smoothness of the surface and of the printing ability of the papers.